Electric heating element



EEEEEEEEEEEEEEEEEEEEE A I. nmcnmu man F55..24,1919.

' Patented 0013. 11, 1921.

uNrrso STATES PATENT OFFICE.

LUTHER D. SMITH, OF TOLEDO, 0H10.

EIC1BIO HEATING ELEMZENT( Application filed February 24, 1919.

tion, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompaning drawings, and tothe characfers of reference marked thereoh, which form a part of this spccification. 7

This invention relates particularly to electrio heating coils of the character in which a current of electricity is passed through a conductor, which ofiers suflcient resistance to the current to produce a required amount of heat under variable conditions .of the electrical voltage,'and has for its primary object t0 render said heating coil or conductor more durable and lasting in use.

It will be understood that the alloys of metal now in common use have various resistance conductivity and that by variations of length and cross section various carrying capacities for creating a desired amount of heat can be obtained, and that alloys such as chromium and nickel are now requently used in single strands of adequate size and length to-obtain desired temperatures when placed in an electric circuit.

It will also be well known that in the preparation and alloying of difierent met-y als uneven results are obtained and that;

when the ailloyed resistor is placed in use, sections of the coil will become hard and brittle and bm-outs readily occur by a high temperature, such as would be generated in the coil by the passage therethrough of a current of higher voltage than it was designed in cross section or length to carry; the frequency of defects and burn-outs depending upon the unequal alloying of the basic materials employed and upon defects in drawing and misuse.

I have discovered that by forming a resistance or heating coi-l of two or more suitable conductors of either pure or alloyed metal and placing them in intimate contacting relation, as by twisting or interweaving them together with two at least thereof of diflerent physical properties or electrical characteristics, the united Specification of Letters Patent.

Patented Oct, 11, 1921.

Serial No. 278,899.

strands or conductors will enduro very considerable variations in voltage, and in case one or more strands burned out because of unequal alloying of the metal or by reason of defects therein, the union is maintained by the other member, acting as a truss wire or support to carry the current across the gap.

Obviously there is nothing new in unitx ing the ends of a broken heating coil by twisting another wire of the same or diferent electrical properties around each end for the purpose of closing the circuit. This is common practice arising from the frequency with which alloyed metals burn out under electrical resistance heat. So far as I know, however, no interwoven or twisted plurality of strands of unlike electrical properties have been employed as a resistance element or heating unit and no auxiliary strand of suitable material has been united with the prime electrical resistance wire or wires to serve as a continuous truss wire theref0r and to form a bridging union where breaks or burn-outs occur therein.

The object of my invention is to produce a heating coil in which these defects shall be overcome in a simple and convenient manner, and while I would not limit myself to the use of any of the common alloys or pure metals now employed, I will, for example, instance the use of 25 feet of #25 gage alloy metal of chromium and nickel in an electric circuit of 110 volts, giving a dissipation of approximately 200 watts and heat sufficient to turn the metal slightlyTed. If this wire is shortened, as commonly donc, to 7 feet in length, it will give approximately 700 watts dissipation and become white hot to a melting point and will last but a very short time in use. I find, bowever, that by twisting or otherwise intimately uniting with the 25 foot length of resistance wire, a wire of different physical properties, as for instance the metal known as monel, and preferably connecting theinterwoven or intimately connected wires in parallel relation in an electric circuit, the coil will dissipate 700 watts and stand the strain of heat without deterioration or burn-outs, even at double the voltage, and that when burn-outs occur, they occur in the alloyed material and not in the truss strand resistant coil. Whfle each strand preferably 'hasflifi'erent physical properties or electrical resistance, two may be of like character if desired, and each of said strands may be'of pure or alloyed metal. Various metals suitable for the purpose can be used. Very atisfactory results are obtained by the use of one strand of alloyed chromium and nickel and another strand of monel metal.

Having thus described my invention, what I daim as new and desire to secure by Letters Patent, is

1. An electric resistance heating clament composed of a plurality of conductors, combined side by side in intimate contact and timately interwoven With one of mone1 metal. v

4:. An electric resistance heating element composed of a plurality of electrica1 conductors, with one of su1table alloy ed meta1 supported and intimately interwen with one of'lower electrical resistance.

' 5. A deice in Which electrical energy is converted into heat, comprising metal conductors intimately connected throughout their effective lengths and having unequal temperature coefiic1ents.

6. An electric resistance heating element composed of a pluralit 0f electrical conductors combined sidey-side in intimate contact, and two at least thereqf having different electrical resistance.

7. An electric resistance heating element composed of twisted cor1ductor strands, two at least of which are of different electrical resistance.

In testimony whereof I have hereunto signed my name to this specification.

' LUTHER D. SMITH. 

